Melanoma is one of the most common cancers in the United States, the incidence of which is rising more rapidly than for any other form of cancer. Melanoma is a malignant tumour of melanocytes, typically of the pigment cells of the skin. However, this cancer may also arise at mucosal surfaces or at other sites to which neural crest cells migrate. Melanomas that have not spread beyond their site of origin are easily cured as these early forms are thin lesions that have not invaded beyond the papillary dermis and can be removed by surgical excision with margins proportional to the stage of the lesion. Some melanomas that have spread to other areas may be curable with wider excision of the primary tumour and removal of the involved regional tumours. However, more advanced forms of melanoma present a high risk of mortality from metastasis to other organs. When metastasis occurs, cancer cells spread via the lymph nodes or blood to distant sites such as the liver, lungs, or brain. The prognosis for patients in the later stages of this disease is poor with average survival from six to ten months.
The ability to cure early stages of melanoma and the fact that it rapidly moves into an incurable metastatic form increases the need for more accurate diagnostic methods for both the early detection of this disease, and for better markers to serve as tools in such diagnostic methods. The problem with devising appropriate therapeutic strategies based on accurate diagnoses and prognoses is that melanoma frequently exhibits unpredictable symptoms and behaviours. For instance, while the vertical thickness of the primary tumour is one of the most important prognostic factors determining survival, many patients with thick melanomas are free of metastasis while a small subset of patients with thin tumours die of their disease.
Currently the diagnosis of malignant melanoma relies upon excision of the affected area and histological examination which leads to many unnecessary biopsies, resulting in discomfort and distress to patients. Diagnosis by eye, based on various clinical features of the lesion is often inaccurate due to the unpredictable features of the disease, and its confusion with conditions such as atypical melanocytic nevi. The use of dermoscopy has also been tried which has improved on the sensitivity and specificity of the diagnosis by eye, however this is still a subjective examination and relies on the expertise of the examiner. Improved markers and resulting tools and methods are therefore required to improve the diagnosis of malignant melanoma to a high degree of accuracy without the need for invasive procedures.
Non-invasive diagnostic tools for malignant melanomas are actively researched and techniques have been developed on the basis of changes in colour, shape, and size of lesions. However, these methods rely on imaging and are still subjective. Further methods using laser Doppler flowmetry (LDF) have also been developed and these are not subjective and have been used to study hypertension, diabetes and anaesthesia. LDF has also been used to study the average blood flow through skin cancers. However, although this method is accurate, the average values are not sufficient to fully characterise blood flow behaviour due to the heterogeneity of skin microvessels and the oscillatory time varying nature of blood flow to tissues across the site of a lesion.
The methods and devices of the present invention aim to overcome at least one or more of the above-mentioned disadvantages of the prior art.